For many years, the problem of disposability has plagued industries which provide disposable items, such as, diapers, wet wipes, incontinent garments and feminine care products. While much headway has been made in addressing this problem, one of the weak links has been the inability to create an economical coherent fibrous web, which will readily dissolve or disintegrate in water, but still have sufficient in-use strength. See, for example, U.K. Patent disclosure 2,241,373 and U.S. Pat. No. 4,186,233. Without such a product, the ability of the user to dispose of the product by flushing it down the toilet is greatly reduced, if not eliminated. Furthermore, the ability of the product to disintegrate in a landfill is quite limited because a large portion of the product components, which may well be biodegradable or photodegradable, are encapsulated in or bound together by plastic which degrades over a long period of time, if at all. Accordingly, if the plastic disintegrated in the presence of water, the internal components could degrade as a result of the rupture of the plastic encapsulation or binding.
Disposable products, such as diapers, feminine care products and adult incontinent care products may be made to be disposed by flushing down toilets. Usually such products comprise a body side liner which must rapidly pass fluids, such as urine or menses, so that the fluid may be absorbed by an absorbent core of the product. Typically, the body side liner may be a coherent fibrous web, which desirably possesses a number of characteristics, such as softness and flexibility. The fibrous web of the body side liner material may be typically formed by wet or dry (air) laying a generally random plurality of fibers and joining them together to form a coherent web with a binder compositions. Past binder compositions have performed this function well. However, fibrous webs comprising these compositions tended to be non-dispersible and present problems in typical household sanitation systems.
Recent binder compositions have been developed which can be more dispersible and are more environmentally responsible than past binder compositions. One class of binder compositions includes polymeric materials having inverse solubility in water. These binder compositions are insoluble in warm water, but are soluble in cold water, such as found in a toilet. It is well known that a number of polymers exhibit cloud points or inverse solubility properties in aqueous media. These polymers have been cited in several publications for various applications, including (1) as evaporation retarders (JP 6207162); (2) as temperature sensitive compositions, which are useful as temperature indicators due to a sharp color change associated with a corresponding temperature change (JP 6192527); (3) as heat sensitive materials that are opaque at a specific temperature and become transparent when cooled to below the specific temperature (JP 51003248 and JP 81035703); (4) as wound dressings with good absorbing characteristics and easy removal (JP 6233809); and (5) as materials in flushable personal care products (U.S. Pat. No. 5,509,913, issued to Richard S. Yeo on Apr. 23, 1996 and assigned to Kimberly-Clark Corporation).
Other recent binders of interest include a class of binders, which are ion-sensitive. Several U.S. and European patents assigned to Lion Corporation of Tokyo, Japan, disclose ion-sensitive polymers comprising acrylic acid and alkyl or aryl acrylates. See U.S. Patent Nos. 5,312,883, 5,317,063 and 5,384,189, the disclosures of which are incorporated herein by reference in their entirety, as well as, European Patent No. 608460A1. In U.S. Pat. No. 5,312,883, terpolymers are disclosed as suitable binders for flushable nonwoven webs. The disclosed acrylic acid-based terpolymers, which comprise partially neutralized acrylic acid, butyl acrylate and 2-ethylhexyl acrylate, are suitable binders for use in flushable nonwoven webs in some parts of the world. However, because of the presence of a small amount of sodium acrylate in the partially neutralized terpolymer, these binders fail to disperse in water containing more than about 15 ppm Ca2+ and/or Mg2+. When placed in water containing more than about 15 ppm Ca2+ and/or Mg2+ ions, nonwoven webs using the above-described binders maintain a tensile strength greater than 30 g/in, which negatively affects the xe2x80x9cdispersibilityxe2x80x9d of the web. The proposed mechanism for the failure is that each calcium ion binds with two carboxylate groups either intramolecularly or intermolecularly. Intramolecular association causes the polymer chain to coil up, which eventually leads to polymer precipitation. Intermolecular association yields crosslinking. Whether intramolecular or intermolecular associations are taking place, the terpolymer is not soluble in water containing more than about 15 ppm Ca2+ and/or Mg2+. Due to the strong interaction between calcium ions and the carboxylate groups of the terpolymer, dissociation of the complex is highly unlikely. Therefore, the above-described polymer that has been exposed to a high Ca2+ and/or Mg2+ concentration solution will not disperse in water even if the calcium concentration decreases. This limits the application of the polymer as a flushable binder material because most areas across the U.S. have hard water, which contains more than 15 ppm Ca2+ and/or Mg2+.
In a co-pending application assigned to Kimberly Clark; i.e., U.S. patent application Ser. No. 09/223,999, filed Dec. 31, 1998 and related case WO/0038751, published on Jul. 6, 2000, the disclosures of which are incorporated herein by reference in their entirety, there is disclosed a modification of the acrylic acid terpolymers of the above-referenced patents to Lion Corporation. Specifically, U.S. patent application Ser. No. 09/223,999 discloses a sulfonate anion modified acrylic acid terpolymers which has improved dispersibility in relatively hard water; e.g., up to 200 ppm Ca2+ and/or Mg2+, compared to the unmodified Lion polymers. However, the Lion Corporation ion-sensitive polymers of the above-referenced patents and the sulfonate anion modified acrylic acid terpolymers of the co-pending application, when used as binders for personal care products, such as wet wipes, typically have reduced sheet wettability, increased sheet stiffness, increased sheet stickiness, reduced binder sprayability and relatively high product cost.
Another approach to dispersible personal care products is disclosed in U.S. Pat. No. 5,281,306 to Kao Corporation of Tokyo, Japan. This patent discloses a water-disintegratable cleansing sheet; i.e., wet wipe, comprising water-dispersible fibers treated with a water-soluble binder having a carboxyl group. The cleansing sheet is treated with a cleansing agent containing 5%-95% of a water-compatible organic solvent and 95%-5% water. A preferred organic solvent is propylene glycol. The cleansing sheet retains wet strength and does not disperse in the organic solvent-based cleansing agent, but disperses in water.
Although many patents disclose various ion and temperature sensitive compositions for water-dispersible or flushable materials, there exists a need for dispersible products possessing softness, flexibility, three dimensionality, and resiliency; wicking and structural integrity in the presence of body fluids (including feces) at body temperature; and true fiber dispersion after toilet flushing so that fibers do not become entangled with tree roots or at bends in sewer pipes. In addition, the known ion-sensitive polymers, such as those of Lion Corporation and the co-pending application of Kimberly Clark, have relatively high viscosities at high shear rates that make application by spraying impossible or impractical. Moreover, there is a need in the art for flushable products having water-dispersibility in all areas of the world, including soft and hard water areas. Furthermore, there is a need for water-dispersible binders that do not reduce wettability of product with which they are used and are sprayable for easy and uniform application to and penetration into products. Finally, there is a need for water-dispersible, flushable wet wipes that are stable during storage and retain a desired level of wet strength during use and are wetted with a wetting composition that is relatively free, or is substantially free, of organic solvents. Such a product is needed at a reasonable cost without compromising product safety and environmental concerns, something that past products have achieved with only limited success.
The present invention is directed to water dispersible fibrous fabrics or material compositions comprising, in part, an ion-sensitive water-dispersible binder which has been developed to address the above-described problems associated with currently available, ion-sensitive polymers and other polymers described in literature. The ion-sensitive compositions of the present invention include polymer formulations which have a xe2x80x9ctrigger property,xe2x80x9d such that the polymers of the fabric are insoluble in a wetting composition comprising ions of a particular type and concentration, such as monovalent salt solutions at a concentration from about 0.3% to about 10%, but can be dispersed when diluted with water, including divalent and/or multivalent salt solutions such as hard water with up to 200 ppm (parts per million, by weight) calcium and magnesium ions. Unlike some ion-sensitive polymer formulations, which lose dispersibility in hard water because of ion cross-linking by calcium ions, the polymer formulations and thus the compositions of the present invention are relatively insensitive to calcium and/or magnesium ions. Consequently, flushable products containing the fabric or compositions of the present invention maintain dispersibility in hard water. Furthermore, the ion-sensitive polymer formulations of the present invention can have improved properties of sprayability or reduced high-shear viscosity, improved product wettability or decreased properties of product stiffness and stickiness.
The products or materials of the present invention are useful structural components for air-laid and wet-laid nonwoven fabrics for applications such as body-side liners, fluid distribution materials, fluid intake materials (surge) or cover stock in various personal care products. The flushable products maintain integrity or wet strength during storage and use, and break apart or disperse after disposal in the toilet when the salt concentration falls below a critical level. Suitable substrates for treatment include, but are not limited to, tissue, such as creped or uncreped tissue, coform products, hydroentangled webs, airlaid mats, fluff pulp, nonwoven webs, and composites thereof. Methods for producing uncreped tissues and molded three-dimensional tissue webs of use in the present invention can be found in commonly owned U.S. patent application, Ser. No. 08/912,906, xe2x80x9cWet Resilient Webs and Disposable Articles Made Therewith,xe2x80x9d by F. J. Chen et al., filed Aug. 15, 1997; U.S. Pat. No. 5,429,686, issued to Chiu et al. on Jul. 4, 1995; U.S. Pat. No. 5,399,412, issued to S. J. Sudall and S. A. Engel on Mar. 21, 1995; U.S. Pat. No. 5,672,248, issued to Wendt et al. on Sep. 30, 1997; and U.S. Pat. No. 5,607,551, issued to Farrington et al. on Mar. 4, 1997; all of which are herein incorporated by reference in their entirety. The molded tissue structures of the above patents can be especially helpful in providing good cleaning in a wet wipe. Good cleaning can also be promoted by providing a degree of texture in other substrates as well by embossing, molding, wetting and through-air drying on a textured fabric, and the like.
Airlaid material can be formed by metering an airflow containing the fibers and other optional materials, in substantially dry condition, onto a typically horizontally moving wire forming screen. Suitable systems and apparatus for air-laying mixtures of fibers and thermoplastic material are disclosed in, for example, U.S. Pat. No. 4,157,724 (Persson), issued Jun. 12, 1979, and reissued Dec. 25, 1984 as Re. U.S. Pat. No. 31,775; U.S. Pat. No. 4,278,113 (Persson), issued Jul. 14, 1981; U.S. Pat. No. 4,264,289 (Day), issued Apr. 28, 1981; U.S. Pat. No. 4,352,649 (Jacobsen et al.), issued Oct. 5, 1982; U.S. Pat. No. 4,353,687 (Hosler, et al.), issued Oct. 12, 1982; U.S. Pat. No. 4,494,278 (Kroyer, et al.), issued Jan. 22, 1985; U.S. Pat. No. 4,627,806 (Johnson), issued Dec. 9, 1986; U.S. Pat. No. 4,650,409 (Nistri, et al.), issued Mar. 17, 1987; and U.S. Pat. No. 4,724,980 (Farley), issued Feb. 16, 1988; and U.S. Pat. No. 4,640,810 (Laursen et al.), issued Feb. 3, 1987.
The present invention also discloses how to make water-dispersible nonwovens, including cover stock (liner), intake (surge) materials and wet wipes, which are stable in fluids having a first ionic composition, such as monovalent ions at a particular concentration greater than is found in typical hard water, using the above-described unique polymer formulations as binder compositions. The resultant nonwovens are flushable and water-dispersible due to the tailored ion sensitivity, which can be triggered regardless of the hardness of water found in toilets throughout the United States and the world. Dispersible products in accordance with the present invention also can have improved properties of softness and flexibility. Such products may also have reduced stickiness. In some embodiments, the polymer formulations with which such articles are treated can have improved properties of sprayability, which improves polymer distribution on the product and penetration into the product, in addition to ease of application, which translates into cost savings.
The present invention also discloses the unexpected benefits obtained where less than about 20%, desirably about 10-15%, of the fibers of the fibrous substrate comprising the water-dispersible fabric have a length of about 6 to about 10 mm, desirably about 7 to about 9 mm, and most desirably about 8 mm. The present invention discloses that where the fabric or composite is comprised of such percentage of fibers having such length that a certain amount of engagement or overlapping (which may also include interweaving and/or entangling) of the fibers occurs that unexpected strength is experienced by the fabric even in the absence of a binder. This is especially true when the Dry Tensile Strength of the material is compared to that of a material having less engagement. This additional sheet strength allows for an increase in processing or line speed of the product. In turn, the increase in processing or line speed of the product allows for an increase in the amount of product produced, thereby contributing to increased profits. It is noted that while the engagement of the fibers provides an increase in dry sheet strength, it does not significantly affect the dispersibility of the sheet, nor does it significantly increase the incidence of tangling or roping. The present invention also provides additional benefit in the production or manufacture of the product in that less binder is needed to achieve and maintain the desired fabric strength characteristics. It has been determined that the present invention provides for the use of less than about 25%, desirably about 5-20%, more desirably about 10-15% by weight binder or glue. The use of less binder in production provides not only for lower costs, but also provides for an increase in the ability to wet the fibers of the substrate at higher sheet speed as well as greater dispersibility speed.
The present invention further discloses an improved wetting composition for wet wipes. Wet wipes employing the fabric or composition of the present invention are stable during storage and retain a desired level of wet strength during use and are wetted with a wetting composition or cleaning agent that can be relatively free, or is substantially free, of organic solvents.
As used herein the following terms have the specified meanings, unless the context demands a different meaning, or a different meaning is expressed; also, the singular generally includes the plural, and the plural generally includes the singular unless otherwise indicated.
As used herein, the term xe2x80x9ccellulosicxe2x80x9d is meant to include any material having cellulose as a major constituent, and, desirably, comprising at least 50 percent by weight cellulose or a cellulose derivative. Thus, the term includes cotton, typical wood pulps, non-woody cellulosic fibers, cellulose acetate, cellulose triacetate, rayon, thermomechanical wood pulp, chemical wood pulp, debonded chemical wood pulp, milkweed, or bacterial cellulose.
As used herein, the terms xe2x80x9ccomprisesxe2x80x9d, xe2x80x9ccomprisingxe2x80x9d and other derivatives from the root term xe2x80x9ccomprisexe2x80x9d are intended to be open-ended terms that specify the presence of any stated features, elements, integers, steps, or components, but do not preclude the presence or addition of one or more other features, elements, integers, steps, components, or groups thereof.
As used herein, the term xe2x80x9cdenierxe2x80x9d means a weight-per-unit-length of any linear material. Specifically, denier is the number of units weights of 0.05 grams per 450 meter length or the weight in grams of 9,000 meters of the material.
As used herein, the term xe2x80x9cfabricxe2x80x9d means a material comprising a network of fibers including, but not limited to, woven or knitted materials, tufted or tufted-like materials, nonwoven webs, and so forth.
As used herein, the term xe2x80x9clayerxe2x80x9d when used in the singular can have the dual meaning of a single element or a plurality of elements.
As used herein, the terms xe2x80x9clotionxe2x80x9d or xe2x80x9cointmentxe2x80x9d are generally interchangeable and mean a formulation, powder or combination thereof comprising skin health ingredients, or compositions which are skin compatible but which do not in and of themselves provide skin health or skin wellness benefits.
As used herein, the term xe2x80x9cmachine-directionxe2x80x9d or MD means the direction of a fabric in the direction in which it is produced. The term xe2x80x9ccross-directionxe2x80x9d or CD means the direction of a fabric generally perpendicular to the MD.
As used herein, the term xe2x80x9cmedicamentxe2x80x9d refers to any compound or composition that provides a benefit or therapeutic effect upon and/or to the skin by physical contact with the skin. This benefit or therapeutic effect can be achieved upon initial application and/or over time with continued use.
As used herein the terms xe2x80x9cnonwovenxe2x80x9d and xe2x80x9cnonwoven fabricxe2x80x9d or xe2x80x9cnonwoven webxe2x80x9d mean a web having a structure of individual fibers, filaments or threads which are randomly arranged or interlaid in a mat-like fashion (including papers), but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as for example, air-laid processes, wet-laid processes, hydroentangling processes, meltblowing processes, spunbonding processes, staple fiber carding and bonding, and solution spinning. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters or sizes useful are usually expressed in microns, denier or decitex (dtex). (Note that to convert from osy to gsm, multiply osy by 33.91).
As used herein, the term xe2x80x9cpersonal care productxe2x80x9d or xe2x80x9cpersonal care absorbent productxe2x80x9d means diapers, training pants, swim wear, absorbent underpants, baby wipes, adult incontinence products, sanitary wipes, wet wipes, feminine hygiene products, wound dressings and bandages and other personal hygiene oriented items.
As used herein, the term xe2x80x9cskin-care additivesxe2x80x9d represents additives, which provide one or more benefits to the user, such as a reduction in the probability of having diaper rash and/or other skin damage caused by fecal enzymes. As used herein, the tern skin-care additives may specifically include, but is not limited to, emollients, lotions, ointments, medicaments, or topical applications.
As used herein, the term xe2x80x9csoft waterxe2x80x9d refers to water having a divalent and/or multivalent ion content of less than about 10 ppm. As used herein, the term xe2x80x9cmoderately hard waterxe2x80x9d refers to water having a divalent and/or multivalent ion content of from about 10 to about 50 ppm. As used herein, the term xe2x80x9chard waterxe2x80x9d refers to water having a divalent and/or multivalent ion content of more than about 50 ppm up to about 200 ppm.
As used herein, the term xe2x80x9ctexxe2x80x9d means a unit for expressing linear density, equal to the weight in grams of 1 kilometer (1000 meters) of yarn, filament, fiber, or other textile strand. As used herein, the term xe2x80x9cdecitexxe2x80x9d or xe2x80x9cdtexxe2x80x9d means a unit for expressing linear density, equal to the weight in grams of 10,000 meters of yarn, filament, fiber, or other textile strand. (Dtex/10=Tex).
As used herein, the term xe2x80x9ctopical applicationxe2x80x9d means any overlayer type of material surface modification, including, but not limited to any polishes, cleaning or cleansing agents, and the like, as well as any lotions, ointments, powders or combinations thereof. For purposes of this application, the term xe2x80x9csurface enhancing agentxe2x80x9d is generally interchangeable with the term topical application.
These terms may be defined with additional language in the remaining portions of the specification.